Delph was a younger member of the Ux. On the planet Ranskoor Av Kolos he was brought by Andinio, his teacher and guardian, to a lake. There his earth moving abilities were tested. However before he could complete this task Tzim-Sha appeared, from nowhere, behind them. Andinio believed Tzim-Sha to be their Creator, but Delph was not sure.
Regardless, Andinio forced him to comply with Tzim-Sha's requests to build him weapons; as this went against everything Andinio taught him about their Creator, Delph tried several times to get her to see she was deluded, but failed. Ultimately, he was forcibly integrated into Tzim-Sha's temple and used to shrink and teleport planets that defied the Stenza to the temple as trophies.
Luckily, Team TARDIS arrived and forced Andinio to see she had been lying to herself. The Thirteenth Doctor made them realise that there was never a "creator" besides themselves. Delph helped Andinio return all the planets, deciding it was best for them to see the rest of the universe. This way they could learn more about the people living in it and to never mistake a horrible monster like Tzim-Sha for a god again. (TV: The Battle of Ranskoor Av Kolos)